With regard to personal authentication, a method using a fingerprint has been widespread for a long time, but recently, as a replacement for visual comparison, various automatic authentication methods in which an image sensor or a semiconductor sensor is combined with image processing by a computer have been developed and widely utilized. Furthermore, recently, a method for personal authentication by reading a subcutaneous vein pattern of a fingertip or the palm of a hand by means of near-infrared light and an image sensor and extracting characteristics such as branching points has been put into practice. However, none of these methods is yet perfect, and the fight against forgery is continuing.
For example, Patent Publications 1 and 2 disclose a clear high-resolution fingerprint sensor using laser light, but this cannot discriminate a forged fingerprint. In contrast thereto, Patent Publication 3 discloses a method in which personal authentication is carried out by a vein pattern using a normal light beam and, furthermore, it is determined whether or not a subject that is authenticated is living by optical detection of the pulse. Although this is not authentication of a fingerprint, it is effective in preventing forgery since it can be confirmed whether the subject that is authenticated is living. However, there are problems with the reliability of authentication by a vein pattern, the complexity of equipment, etc.    (Patent Publication 1) JP-A-5-73666 (JP-A denotes a Japanese unexamined patent application publication)    (Patent Publication 2) JP-A-8-16752    (Patent Publication 3) JP-A-2003-331268
On the other hand, it is known that, when laser light is shone on a living body, the intensity distribution of reflected scattered light thereof forms a dynamic laser speckle (random spot pattern) due to moving scattering particles such as blood cells; this pattern is detected on an imaging plane by an image sensor, and by quantifying changes over time of the pattern in each pixel and displaying them as a map, it is possible to image the blood flow distribution of capillary vessels in the vicinity of the surface of the living body. Using such a phenomenon, techniques and devices for measuring a blood flow map of the area underneath the skin or of the ocular fundus have been proposed by the present inventors (ref. e.g. Patent Publications 4 to 9).    (Patent Publication 4) JP-B-5-28133 (JP-B denotes a Japanese examined patent application publication)    (Patent Publication 5) JP-B-5-28134    (Patent Publication 6) JP-A-4-242628    (Patent Publication 7) JP-A-8-112262    (Patent Publication 8) JP-A-2003-164431    (Patent Publication 9) JP-A-2003-180641
The present inventors have carried out an intensive investigation into the concept of combining a blood flow map and a fingerprint pattern for use in personal authentication, and have already proposed a personal authentication method involving measuring subcutaneous blood flow and means therefor. That is, there have been proposed a personal authentication method comprising (1) a step of imaging, on an image sensor as a laser speckle using an optical system, light reflected from a subcutaneous blood vessel layer when a laser beam is expanded and made to irradiate a finger pad, (2) a step of determining a quantity that represents the rate of a change with respect to time of the amount of light received for each pixel of the laser speckle, for example, the average rate of change with respect to time, or the reciprocal of the magnitude of the variation in the amount of light received integrated over the exposure time of the image sensor, and obtaining a finger pad blood flow map as a two-dimensional map of numerical values thereof, and (3) a step of comparing and evaluating a fingerprint pattern represented as a blood flow map against pre-registered personal data, and devices for carrying out each step (Patent Publication 10).    (Patent Publication 10) International Patent Application WO2005/122896
Furthermore, the present inventors have improved the above-mentioned methods, and have invented a method and means in which a fingertip is irradiated with one laser beam at a specific wavelength as irradiation light, or with a plurality of laser beams at different wavelengths at the same time or in sequence to give a superimposed blood flow rate map or a plurality of blood flow rate maps with respect to reflected light (PCT/JP2007/050060). The depth of penetration of a laser into tissue depends on the wavelength of the laser; with light having a short wavelength such as visible light, only a blood flow distribution close to the surface, that is, a fingerprint pattern, is obtained, but since light having a long wavelength such as near-infrared light enters deep into the tissue, a blood flow map reflecting a blood flow distribution in the interior can be obtained. There is a difference in blood flow distribution in the interior between individuals, and since it is difficult to forge, if this is added to authentication data the accuracy of personal verification is improved due to a synergistic effect.
Conventionally, a method and a device for forming signature data or a password by coding and encrypting personal biological information, for example, information from a photographic image of the ocular fundus, have been proposed (ref. Patent Publications 11 to 12).
However, no proposal has been made so far for a combination of blood flow data such as the course of blood vessels on the retina and the distribution profile of arteries and veins and, furthermore, distribution in a choroid blood vessel layer present behind the retina and a change in blood flow over time obtained by imaging of ocular fundus blood flow with the personal authentication method previously proposed by the present inventors.    (Patent Publication 11) JP-A-11-215119    (Patent Publication 12) JP-A-11-149453